It is known that the performance of wireless communications systems, and particularly mobile cellular systems, can be affected by a number of factors. Generally, such cellular systems are operated over these factors to achieve an optimum ratio of signal strength to interference (C/I) for the reception experienced by each mobile user while still providing enough capacity throughout the system.
Recent advances have been made in addressing various of these individual factors that affect reception performance. The emergence of Code Division Multiple Access (CDMA) as a method of broadcasting multiple signals simultaneously on a single broad frequency band throughout the system has remediated problems of co-channel interference and multi-path fading. The arrival of CDMA has also simplified cell-to-cell handoff procedures, creating a "soft" handoff that eliminates frequency assignment and management.
Improvements in cellular capacity and call quality through the use of coordinated multiple antennas are also now known. For example, above-referenced copending and commonly assigned U.S. Patent applications APPARATUS, SYSTEMS AND METHODS FOR ANTENNA COMBINING IN WIRELESS COMMUNICATIONS SYSTEMS and MULTIPLE ANTENNA TRANSMISSION SYSTEM teach substituting multiple narrow-beam antenna configurations for traditional single or three-face base-station antennas. According to these inventions, the use of time delay techniques with summing of the received CDMA signal allows the output of multiple antennas to be combined and interpreted by receiver technology standard in the art. Among other improvements, these inventions allow assignment of a narrow transmission beam between the base station and the mobile, thereby reducing the potential for signal interference and facilitating forward-link and reverse-link power management.
Further innovation is taught in above-referenced co-pending, commonly assigned U.S. Patent application SYSTEM AND METHOD FOR FREQUENCY MULTIPLEXING ANTENNA SIGNALS, in which the down-mixing and subsequent up-mixing of the outputs of multiple antenna signals with pre-selected local oscillator frequencies permit said signals to be combined and carried simultaneously on a reduced number of antenna cables.
A need now exists for an intelligent control system that will synergize the advantages offered by some of the foregoing recent innovations, thereby providing overall improved wireless service to the mobile user.
Moreover, the current art recognizes that cells in a cellular system also typically act autonomously within parameters set for the cellular system. The exception is in regard to handoff, where neighboring cells will typically coordinate a channel change as a mobile enters a new cell. Especially in high interference environments, however, autonomous cell operation, substantially without reference to neighboring cells, can increase the potential for co-channel interference, possibly causing signal quality degradation or, worse still, loss of call or assignment of the signal to the wrong mobile.
Currently, the possibility of such co-channel interference is minimized by devising cell re-use patterns that adopt "worst case assumptions" about required channel bandwidth separation and physical spatial separation of cells. The available spectrum for each carrier normally consists of a plurality of channels combined into 21 channel sets. These channel sets are than separated by a maximum physical distance in order to reduce co-channel interference. Since each cell is generally comprised of three 120-degree sectors, each sector has only seven channel sets to work with. Typically, a passive channel re-use pattern is devised whereby it is left to a predetermined configuration of physical cell separation and neighboring channel allocation to minimize the potential for co-channel interference.
An intelligent control system, in which cell operation and channel assignment is actively inter-coordinated, would therefore also enhance cellular capacity. Further, by utilizing narrow beam technology such as disclosed in the above-referenced co-pending commonly assigned U.S. patent application, dynamic beam control and power management could be combined with interactive channel assignment to provide a system with optimum capacity and reduced signal interference.